The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.
Coal mining is performed to extract coal, lying in seams, from the ground. Many techniques have been employed to extract coal seams over the years, varying from tunneling though to large open cut mines. Two contemporary underground coal mining techniques include long wall mining, and bord and pillar mining as described below.
Long wall mining is a form of underground mining where a block of coal is mined using a moving long wall. A number of hydraulic jacks, called chocks, are placed in a long line in order to support the overlying strata (ie. the roof) at the coalface. The coal is then cut from the coalface by a machine called a shearer which travels back and forth along the long wall face in advance of the chocks, which move consecutively ahead to fill in the roof void created by the shearer as it completes its coal cutting pass.
Although the capital expense in setting up a long wall mine is very high, the operating cost is generally quite low. However, the long wall movement can be stifled in the event of an interrupted coal seam along a fault line which can undesirably greatly add to the operating cost and cause production disruptions. In addition, whilst mining personnel are generally working under fully supported roof (or chocks) most of the time, they are nevertheless required to work in close proximity to large and hazardous moving hydraulic and electrical equipment, near to the coal cutting face generally also in high airflow ventilation areas, and are as a result exposed to a variety of mining and environmental hazards.
Bord and pillar mining is initially less capital intensive than long wall mining. The coal seam is divided into a regular block like array by driving through tunnels termed “bords”. The blocks of coal bounded by the bords are the “pillars”. The pillars support the overlying strata during the “first workings” as the bords are created, and may be partially extracted systematically during the “second workings” upon retreat from the mine. Owing to the fact that the bord and pillar mining process is more labour intensive and has lower productivity than in longwall mining, in addition to the fact that not all of the coal is extracted, the overall operating costs of bord and pillar mining are substantially higher than long wall mining. In addition, mining personnel are required to work in confined spaces, in close proximity to large hazardous moving equipment, in areas where they may be inadequate roof or coal rib support and possibly with poor ventilation in blind tunnels. As a result they are exposed to a greater level of mining and environmental hazards than that of long wall mining.
The preferred embodiment provides an alternative mining method with lower initial capital costs than long wall mining, yet with improved productivity, a higher level of coal extraction and substantially reduced operating costs when compared with bord and pillar mining. Importantly also, mining personnel are generally remote from the mining process at the coal cutting face and are not exposed to the same level of mining or environmental hazards as those in either long wall or bord and pillar operations.